The present invention relates to a method for starting a multi-cylinder internal combustion engine, especially of a motor vehicle wherein the position of a piston in a cylinder of the engine is determined. Fuel is injected into a combustion chamber of that cylinder whose piston is in a work phase.
The invention furthermore relates to a multi-cylinder internal combustion engine, especially of a motor vehicle. The internal combustion engine includes a detector device for determining the position of a piston in a cylinder of the engine and a fuel metering system for injecting fuel into a combustion chamber of that cylinder whose piston is in a work phase. Finally, the present invention relates also to a control apparatus for such a multi-cylinder internal combustion engine, especially of a motor vehicle.
A method for starting a multi-cylinder internal combustion engine of the kind described above is known, for example, from DE 31 17 144 A1. The method described therein operates without an electric-motoric starter. At standstill of the engine, a quantity of fuel, which is necessary for a combustion, is injected and ignited in the combustion chamber of one or several cylinders whose piston is disposed in the work phase. Thereafter, fuel is injected and ignited in each of the combustion chamber(s) of the cylinders whose pistons execute the next work stroke as soon as the particular piston has reached the work position. In this way, the internal combustion engine can be configured without an electric starter and the components necessarily associated therewith. In addition, an electric storage battery of the engine can be dimensioned smaller because this battery no longer has to supply energy for the starter and the other electrical components.
In the known method for starting an internal combustion engine, the stroke (compression stroke, work stroke, discharge stroke, induction stroke) in which the individual pistons of the engine and the inlet and outlet valves of the combustion chamber are disposed must be precisely observed. This has the consequence that, in a 4-cylinder or 6-cylinder engine, for each stroke of the engine, only the combustion chamber of a single cylinder (namely, of the cylinder whose piston is in the work position) can be filled with fuel and the fuel can be ignited. The known method is limited to internal combustion engines wherein, on the one hand, the compression stroke, work stroke, discharge stroke and induction stroke are run through in a fixed sequence per cylinder and wherein, on the other hand, the distribution of the strokes to the individual cylinders is fixedly pregiven.
As a further state of the art, reference is made U.S. Pat. No. 6,050,232 A1 from which likewise a method is known for starting an internal combustion engine without an electric starter.
The present invention has the task of starting a multi-cylinder internal combustion engine without an electric starter in the simplest possible way, rapidly and yet reliably.
For solving this task, the invention proceeds from the method of the art mentioned initially herein and suggests that the inlet and/or outlet valves of at least one cylinder whose piston is disposed after top dead center is brought into a position corresponding to a work phase in advance of the start operation.
The method of the invention includes, for example, a camshaft-free control of the inlet and/or outlet valves. In this way, each inlet valve and outlet valve can be driven separately from the other valves and independently of the position of the camshaft. For a camshaft-free control, the inlet and/outlet valves are equipped individually or several in common with an actuator element. The actuator element can be operated hydraulically, piezoelectrically, electromagnetically, or in another way. A plurality of camshaft-free controls for the inlet and outlet valves are known from the state of the art, which can be utilized in combination with the present method according to the invention.
Alternatively, the method according to the invention includes, for example, a variable camshaft positioning device on the inlet end in order to adjust an early inlet closure of the inlet valve. The inlet camshaft can be so displaced that the inlet valves are opened in the induction phase only at the start for a short time and are thereby brought into a position corresponding to the work phase. In this way, an earlier inlet closure can be adjusted at the inlet end.
In the method according to the invention, the valves can be independently and, insofar as the free movement of the valve permits, freely opened or closed. In this way, it is achieved to change from an induction phase into a work phase and vice versa in advance of or during the starting operation. In the same manner, the change from a compression phase to a discharge phase and vice versa, is possible.
With the method of the invention, it is possible for the first time in a four or six-cylinder engine, at the beginning of the start operation, to bring two cylinders into the position corresponding to the work phase. Fuel is injected simultaneously into the combustion chambers of these two cylinders and the air/fuel mixture is simultaneously ignited. The double combustion leads to an especially intense start acceleration of the crankshaft and therefore to an especially short start operation. The double combustion offers adequate reserve in order to reliably overcome possible friction and compression resistances at the beginning of the start operation.
Fuel is then injected into the combustion chamber of a further cylinder disposed in the compression phase and the compressed air/fuel mixture is ignited. The injection begin in the combustion chamber of the additional cylinder can, if the injection pressure is high enough, be shifted into the advancing compression phase until shortly before reaching top dead center. Because of the second combustion, the rotational movement of the crankshaft is further accelerated. During the further course of the start operation, fuel is injected into the combustion chambers of cylinders disposed in the induction phase and the compressed air/fuel mixture, which is disposed in the combustion chambers, is ignited. Here too, the injections can take place alternatively also during the compression phase if the injection pressure is sufficiently high.
According to an advantageous embodiment of the present invention, it is suggested that:
the inlet and/or outlet valves of a further cylinder, whose piston is disposed ahead of top dead center, are brought into a position corresponding to a compression phase;
fuel is injected into the combustion chamber of the at least one cylinder disposed in the work phase;
the fuel, which is injected into the at least one cylinder, is ignited in the work phase;
fuel is injected into the combustion chamber of the additional cylinder disposed in the compression phase;
the fuel, which is compressed in the combustion chamber of the additional cylinder, is ignited; and,
in the further course of the starting operation, fuel is injected into the combustion chambers of cylinders disposed either in an induction phase or in a compression phase and the fuel, which is compressed in the combustion chambers, is ignited.
By igniting the fuel, which is injected into at least one cylinder in the work phase, a combustion is effected via which a forwardly directed rotational movement is imparted to the crankshaft of the engine. This rotational movement is continued or even accelerated by the ignition of the fuel compressed in the combustion chamber of the additional cylinder.
Finally, in the further course of the starting operation, fuel is injected into the combustion chambers and the fuel, which is compressed in the combustion chambers (that is, at the end of the compression phase or at the start of the work phase) is ignited. In the further course of the starting operation, the fuel is injected in the induction phase or, if the injection pressure is sufficiently high, into the combustion chambers in the compression phase. The starting operation is preferably continued so long until the engine is started and runs automatically in the normal operation.
According to an especially advantageous embodiment of the present invention, it is suggested that:
the inlet and/or outlet valves of two cylinders whose pistons are after top dead center, are brought into a position corresponding to a work phase;
fuel is injected into the combustion chambers of the two cylinders disposed in the work phase; and,
the fuel, which is injected into the two cylinders, is ignited in the work phase.
This embodiment permits a double combustion which leads to an especially intense starting acceleration of the crankshaft and therefore to an especially short starting operation.
According to a preferred embodiment of the present invention, it is suggested that the inlet and/or outlet valves of the combustion chambers be brought into the position corresponding to the work phase by means of a camshaft-free control.
Alternatively, it is suggested that the inlet and/or outlet valves of the combustion chambers are brought into the position corresponding to the work phase via such a shift of an inlet camshaft of a variable camshaft actuator device that the inlet valves in an induction phase are opened for a short time only at the beginning. In this way, an earlier inlet closure can be adjusted at the inlet end. In a 4-cylinder engine, two cylinders are thereby disposed at the beginning of the starting operation in the position corresponding to the work phase. Fuel is injected simultaneously into the combustion chambers of these two cylinders and the air/fuel mixture is simultaneously ignited. The double combustion leads to an especially intense starting acceleration of the crankshaft and therefore to an especially short starting operation.
From the method according to the invention, additional degrees of freedom result in the starting operation which can be used in accordance with the invention, inter alia, to initiate a second starting attempt after an unsuccessful first ignition. According to a preferred embodiment of the present invention, it is suggested that, after an unsuccessful first ignition of the fuel, which is injected into at least one cylinder, in the work phase, the method is carried out once again with inverted phases of the individual cylinders. The first ignition is, for example, unsuccessful when the engine does not move or a first compression resistance of the cylinder could not be overcome. In such a case, the method according to the invention is executed once more but with inverted phases of the individual cylinders. This means that the inlet and outlet valves which have been brought into the position corresponding to the work phase in the first start attempt, are now brought into a position corresponding to the induction phase. Likewise, the inlet and outlet valves, which had been brought into a position corresponding to a compression phase, are now brought into a position corresponding to the discharge phase. In the second starting attempt, the injection of fuel into the combustion chambers and the ignition of the fuel, which is compressed in the combustion chambers, takes place in the manner described above.
According to an advantageous further embodiment of the present invention, it is suggested that the pistons of the cylinders are brought into a pregivable start position at the beginning of the start operation. In this way, it can be ensured even for internal combustion engines having fewer than four cylinders, that the piston of at least one cylinder of the engine is disposed in a position optimal for carrying out the starting operation according to the invention. In this way, during the starting operation, a maximum starting acceleration of the crankshaft can be generated with the first combustion. To move the pistons in the cylinders, an electric-motoric starter can be used, which operates on the crankshaft of the engine and rotates the same.
According to a preferred embodiment of the present invention, it is suggested that the fuel, which is compressed in a combustion chamber of a cylinder, is ignited shortly before reaching top dead center of the piston of the particular cylinder toward the end of the compression phase. Alternatively, the compressed fuel can also be ignited shortly after or at the top dead center of the piston of the particular cylinder.
Advantageously, the fuel is injected into the combustion chambers during the starting operation by a presupply pump of the fuel metering system. The presupply pump is, for example, configured as an electric fuel pump driven independently of the internal combustion engine. A presupply pump functions, for example, in a common rail fuel metering system to pump fuel from a fuel supply vessel into a low pressure region of the fuel metering system.
Alternatively, it is suggested that the fuel be injected into the combustion chambers during the starting operation via a high pressure pump of the fuel metering system which is driven independently of the internal combustion engine. In a common rail fuel metering system, the high pressure pump, for example, pumps fuel from the low pressure region of the fuel metering system at high pressure into a high pressure store. From the high pressure store, injection valves branch away via which the fuel is injected from the high pressure store into the combustion chambers of the cylinders. The high pressure pump can, for example, be driven electrically. With the aid of a high pressure pump, especially high injection pressures can be achieved during the starting operation so that the injection time point during the starting operation can be shifted easily into the advanced compression phase up to shortly before reaching top dead center.
To reduce the compression resistance during the starting operation according to the invention, it is suggested in accordance with a preferred embodiment of the present invention that, during the starting operation, in a compression phase of a cylinder of the engine, the corresponding inlet valve of the cylinder is closed delayed or too early. In this way, each run-through compression phase can be shortened in an advantageous manner via a delayed closing of the corresponding inlet valves. These valves are open during the induction phase which takes place in advance of the compression phase. In this way, the crankshaft of the engine can be transferred substantially easier into a rotational movement via the first combustion at the beginning of the starting operation according to the invention and the engine is started. For the same purpose, alternatively, during the starting operation in an induction phase of a cylinder of the engine, the corresponding inlet valve of the cylinder can be closed delayed or too early.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an engine, especially of a motor vehicle. A program is stored on the control element which is capable of being run on a computer, especially on a microprocessor, and is suitable for executing the method according to the invention. In this case, the invention is realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method which the program can carry out. Especially an electric storage medium can be used as a control element, for example, a read-only-memory or a flash memory.
As a further solution of the task of the present invention and proceeding from the multi-cylinder internal combustion of the kind mentioned initially herein, it is suggested that the engine include means for displacing inlet and/or outlet valves of at least one cylinder, whose piston is disposed after top dead center, into a position corresponding to a work phase in advance of the starting operation.
According to an advantageous embodiment of the present invention, it is suggested that the internal combustion engine include a camshaft-free control of inlet and/or outlet valves of the combustion chambers.
Alternatively, it is suggested that the internal combustion engine has, at the inlet end, a variable camshaft positioning device for adjusting an early inlet closure of the inlet valves.
According to a preferred embodiment of the present invention, it is suggested that the internal combustion engine include means for moving the pistons of the cylinders into a pregivable start position at the beginning of the starting operation.
Finally, it is suggested that the fuel metering system has a high pressure pump, which is driven independently of the engine, to build up a fuel injection pressure.
As still another solution of the present invention starting with the control apparatus of the type referred to initially herein, the control apparatus includes means for executing the method of the invention. The control apparatus, to start an internal combustion engine, carries out a drive of components of the engine participating in the starting operation according to the invention, especially components of the fuel metering system and the ignition. The control apparatus obtains the command for starting the internal combustion engine, for example, via the actuation of an ignition key or a starter button.
Further features, application possibilities and advantages of the invention will become apparent from the following description of embodiments of the invention which are illustrated in the drawing. All described or illustrated features define the subject matter of the invention by themselves or in any desired combination independently of their summary in the patent claims or their dependency as well as independently of their formulation or presentation in the description and/or in the drawing.